linux-kernel - Re: [PATCH 1/3] ata: sata_dwc_460ex: use "dmas" DT property to find dma channel

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Message-ID: <yw1xlh8r9wkm.fsf@unicorn.mansr.com>
Date:	Fri, 18 Dec 2015 23:16:41 +0000
From:	Måns Rullgård <mans@...sr.com>
To:	Julian Margetson <runaway@...dw.ms>
Cc:	Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
	Tejun Heo <tj@...nel.org>, linux-ide@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/3] ata: sata_dwc_460ex: use "dmas" DT property to find dma channel

Julian Margetson <runaway@...dw.ms> writes:

> On 12/18/2015 6:33 PM, Måns Rullgård wrote:
>> Julian Margetson <runaway@...dw.ms> writes:
>>
>>> On 12/18/2015 1:18 PM, Måns Rullgård wrote:
>>>> Julian Margetson <runaway@...dw.ms> writes:
>>>>
>>>>> On 12/18/2015 8:49 AM, Måns Rullgård wrote:
>>>>>> Andy Shevchenko <andriy.shevchenko@...ux.intel.com> writes:
>>>>>>
>>>>>>>>> [    5.206125] Unable to handle kernel paging request for data at
>>>>>>>>> address 0x00000000
>>>>>>>>> [    5.228546] Faulting instruction address: 0xc043a2c8
>>>>>>>>> [    5.248577] Vector: 300 (Data Access) at [eddafae0]
>>>>>>>>> [    5.268658]     pc: c043a2c8: sata_dwc_qc_issue+0xb8/0x204
>>>>>>>> Well, that's not good.  Can you translate that address to a line of
>>>>>>>> code?
>>>>>>> Besides that, can you enable DYNAMIC_DEBUG in the config and append
>>>>>>> 'dw_dmac_core.dyndbg dw_dmac.dyndbg' to the kernel cmdline?
>>>>>> Enabling debug messages in the sata_dwc driver might also be informative.
>>>>>>
>>>>> Changed the sata-dwc to a module .
>>>>>
>>>>> [   18.475140] sata-dwc 4bffd1000.sata: sata_dwc_qc_prep_by_tag: dma_dwc_xfer_setup returns NULL
>>>>> [   18.535698] sata-dwc 4bffd1000.sata: sata_dwc_qc_prep_by_tag: dma_dwc_xfer_setup returns NULL
>>>> That's strange.  The only way that can happen is if
>>>> dmaengine_prep_slave_sg() return NULL, and that really shouldn't be
>>>> happening.  Did you turn on debug messages in dw_dma?  You can enable
>>>> some extra debug messages by adding "#define VERBOSE_DEBUG" at the top
>>>> of drivers/dma/dw/core.c
>>>>
>>> [   17.526173] sata-dwc 4bffd1000.sata: sata_dwc_qc_prep_by_tag: dma_dwc_xfer_setup returns NULL
>>> [   17.600124] sata-dwc 4bffd1000.sata: sata_dwc_qc_prep_by_tag: dma_dwc_xfer_setup returns NULL
>>> [   17.662978] sata-dwc 4bffd1000.sata: sata_dwc_qc_prep_by_tag: dma_dwc_xfer_setup returns NULL
>> Could you post the entire kernel log?  There might be important
>> information before the errors start.
>>
>
>
> =~=~=~=~=~=~=~=~=~=~=~= PuTTY log 2015.12.18 15:01:48 =~=~=~=~=~=~=~=~=~=~=~=
> [    0.000000] Using Canyonlands machine description
> [    0.000000] Initializing cgroup subsys cpu
> [    0.000000] Linux version 4.4.0-rc5-Sam460ex (root@...ian-VirtualBox) (gcc version 4.8.2 (Ubuntu 4.8.2-16ubuntu3) ) #8 PREEMPT Fri Dec 18 13:36:34 AST 2015
> [    0.000000] Zone ranges:
> [    0.000000]   DMA      [mem 0x0000000000000000-0x000000002fffffff]
> [    0.000000]   Normal   empty
> [    0.000000]   HighMem  [mem 0x0000000030000000-0x000000007fffffff]
> [    0.000000] Movable zone start for each node
> [    0.000000] Early memory node ranges
> [    0.000000]   node   0: [mem 0x0000000000000000-0x000000007fffffff]
> [    0.000000] Initmem setup node 0 [mem 0x0000000000000000-0x000000007fffffff]
> [    0.000000] MMU: Allocated 1088 bytes of context maps for 255 contexts
> [    0.000000] Built 1 zonelists in Zone order, mobility grouping on.  Total pages: 522752
> [    0.000000] Kernel command line: root=/dev/sda8 console=ttyS0,115200 console=tty0 dw_dmac_core.dyndbg dw_dmac.dyndbg

[...]

> [   13.643415] systemd[1]: Mounted Configuration File System.
> [   17.526173] sata-dwc 4bffd1000.sata: sata_dwc_qc_prep_by_tag: dma_dwc_xfer_setup returns NULL
> [   17.600124] sata-dwc 4bffd1000.sata: sata_dwc_qc_prep_by_tag: dma_dwc_xfer_setup returns NULL
> [   17.662978] sata-dwc 4bffd1000.sata: sata_dwc_qc_prep_by_tag: dma_dwc_xfer_setup returns NULL

This log is weird.  The sata_dwc_probe() function prints several things
(one using dev_notice()), for instance this:

	/* Read the ID and Version Registers */
	idr = in_le32(&hsdev->sata_dwc_regs->idr);
	versionr = in_le32(&hsdev->sata_dwc_regs->versionr);
	dev_notice(&ofdev->dev, "id %d, controller version %c.%c%c\n",
		   idr, ver[0], ver[1], ver[2]);

The dw_dma_probe() function also prints a line:

	dev_info(chip->dev, "DesignWare DMA Controller, %d channels\n",
		 pdata->nr_channels);

These messages are nowhere to be seen in your log, nor are numerous
others that really must appear before before sata_dwc_qc_prep_by_tag()
can be called.

I'd like to note that the driver works on my Sigma Designs based system
using a different DMA controller, so it's not completely broken.  The
DMA driver could still be faulty, but that still doesn't explain the
missing kernel messages.

-- 
Måns Rullgård
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